1. Field of Invention
This invention relates to generally to electronic systems and more specifically to test systems.
2. Discussion of Related Art
Test systems are often used to verify the performance of electronic devices. An electronic device (sometimes referred to as a Unit Under Test) may be tested as a stand alone unit or may be integrated into a test environment that simulates the operating conditions of the device. The test environment may include a digital test instrument that generates and measures digital signals provided to the unit under test. The test environment may also include power supplies and instruments that generate and measure analog signals to be able to fully simulate the intended operating environment of the unit under test.
The Unit Under Test (UUT) typically goes through a testing phase performed by Automatic Test Equipment (ATE). ATE operates under the control of test software, often running on a host computer. The ATE is programmed to provide stimulus to a particular circuit or component in the UUT and then measure the output to determine if the UUT has performed to its specifications. ATE may include a digital test instrument that has multiple digital channels. Each digital channel may include a driver and a detector to generate and/or measure a digital signal. The driver output and detector input may be connected together to allow for bi-directional operation.
The driver circuit usually has two or more user programmable levels. Programmable drive levels allow the tester to emulate the logic family of any device they are testing. Most logic families require only two drive levels to account for a logic high and a logic low. An additional drive level can be used as an idle state or a termination level when receiving a signal.
The detector circuit usually has two user programmable thresholds. Although a single threshold can be used to specify the logic state that the UUT is driving, dual-threshold detection is often used in digital channels of test equipment to verify that the UUT is driving or receiving voltages above the specified high voltage or below the specified low voltage. Conformance to these voltage specifications is required to reliably test the UUT.
Some test instruments include protective circuitry that isolates circuitry in the test instrument from an input when the voltage and/or current applied at the input exceeds a rated value. Traditional and solid state fuses are used for this purpose. Also, switches have been used along with a voltage sensing circuit that activates the switch to disconnect the test instrument from an input when the voltage or current at the input exceeds a specific value.
It would be desirable to have an improved test system.